1. Field of the Invention
The present invention relates to a thin-film transistor liquid crystal display device, and deals with abnormality in the operation of a thin-film transistor.
2. Description of the Related Art
A liquid crystal display element comprises a liquid crystal material interposed between two substrates that have been oriented, with the peripheral edges being sealed by a seal. The liquid crystal display element performs display as a result of the state of orientation of the liquid crystal material interposed between the two substrates being controlled. The techniques for controlling this state of orientation are various, but a technique is widely and commonly performed where the state of orientation of the liquid crystal material in a steady state is controlled by the orientation of the surfaces of the two substrates and where an electric field is applied to the liquid crystal material by an electrode disposed on at least one of the substrates to cause the liquid crystal material to change from its steady state.
In a thin-film transistor (TFT) liquid crystal display device, data signal lines that send data corresponding to a voltage level applied to the liquid crystal of each pixel and scan signal lines that control the writing of data signals to each pixel are wired in the vertical direction and the horizontal direction of a screen, and one or more transistors are connected to each of the pixels arranged in a matrix.
When an operation abnormality occurs in these transistors, a bright spot defect or a black spot defect occurs depending on the relationship between the content of the abnormality and the operation mode of the liquid crystal. There are various methods for repairing these defects, but it is difficult to repair a transistor whose operation has become abnormal, and black spot repair that abandons drive operation resulting from a transistor and wires a pixel electrode to another line and a method that wires a pixel electrode to another pixel electrode to perform the same display with two pixels and make the defect inconspicuous are common.
In this manner, when an abnormality in the operation of a transistor occurs, the abnormal transistor is cut off from the pixel electrode and, at the same time, the pixel electrode is connected to another line or an adjacent pixel electrode to make the defect inconspicuous.
Further, in JP-A-5-341316, connecting two transistors to one pixel and cutting off a transistor that has become abnormal is described.
Thus, it is an object of the present invention to provide a liquid crystal display device where operational abnormalities in thin-film transistors are eliminated.
When, in order to repair a defect in a display device resulting from an abnormality in the operation of a thin-film transistor, the pixel connected to the operationally abnormal transistor is cut off from the operationally abnormal transistor, connected to another line, and becomes a black spot, the pixel that has become a black spot continues to display black regardless of the screen that is to be originally displayed.
In a color liquid crystal display device, pixels having color filters of three or more color light up at the same time and display white, so that if a black spot in one color occurs, that one color does not light up in the white display state and ends up appearing as a complementary color of the color that does not light up. Particularly in uses such as a liquid crystal television where the pixel size is large, even a black spot defect ends up appearing as a colored spot defect in the white display.
Further, the method of cutting off a pixel connected to an operationally abnormal transistor from the operationally abnormal pixel and connecting the pixel to an adjacent pixel is effective when displaying white, but when red, green, and blue are displayed using a color filter of a single color, a phenomenon occurs where a pixel that is not supposed to light up ends up lighting up or a pixel that is supposed to light up ends up not lighting up, so it is difficult to say that the repair is infallible.
Moreover, the method of connecting two transistors to one pixel cannot be employed in large-screen high-definition products because parasitic capacitance between the gate lines and the data lines becomes large, the problem of signal delay occurs, and the brightness within the screen becomes non-uniform.
In this manner, even when operation of a thin-film transistor is abnormal, it is necessary to realize white color display that is uniform within the screen, single color display that is uniform within the screen, and brightness display that is uniform within the screen.